Protection apparatus applied to a telephone line

Abstract

A protection device applied to a telephone line comprises at least an overload detecting device, a high temperature detecting circuit, and an enforcing on-hook means. When an abnormal over voltage or over current occurs, it can be detected by the overload detecting device. An overload signal is output to the enforcing on-hook device. Or when the temperature of a fax/modem machine raises abnormally, it can be detected by the high temperature detecting circuit. A high temperature signal is then output to enforcing on-hook device. While the enforcing on-hook device receives the overload signal or the high temperature signal, the system is on hook.

What is claimed is:  
     
       1. An over voltage/current protection apparatus suitable for use in a telephone line, the protection apparatus being coupled with the telephone line which provides a telephone line voltage, the protection apparatus comprising: 
       a bridge rectifier, for rectifying the telephone line voltage into a rectified voltage and coupled to the telephone line;  
       overload detecting means, coupled to the bridge rectifier for receiving the rectified voltage, the overload detecting means outputting an overload signal when the rectified voltage exceeds a predetermined value or an overcurrent is detected;  
       enforcing on-hook means, coupled to the overload detecting means for receiving the overload signal, and outputting an on-hook signal according to the overload signal; and  
       a hook switch, coupled to the on-hook means and connected to the telephone line in series, to perform an on-hook operation on a telephone according to the on-hook signal,  
       wherein the overload detecting means comprises:  
       a first resistor (R 2 ), coupled to a positive voltage output terminal of the bridge rectifier and a first node (a 1 );  
       a second resistor (R 3 ), coupled to the first node (a 1 ) and a negative output terminal of the bridge rectifier;  
       a first capacitor (C 1 ), coupled to the first node (a 1 ) and the negative voltage output terminal of the bridge rectifier;  
       a photo-coupler (U 1 ), having a third lead coupled to ground and a fourth lead to the enforcing on-hook means;  
       a third resistor (R 1 ), coupled to the positive output terminal of the bridge rectifier and a first lead of the photo-coupler;  
       a first transistor (Q 1 ), having a collector connecting to a second lead of the photo-coupler, an emitter connecting to the negative output terminal of the bridge rectifier and a base connecting to the first node (a 1 ).  
     
     
       2. The protection apparatus according to claim  1 , comprising further a fax/modem controller to detect an operation status and output the on-hook signal. 
     
     
       3. The protection apparatus according to claim  2 , wherein the photo-coupler is used to output the overload signal when the rectified voltage is higher than the pre-determined value. 
     
     
       4. The protection apparatus according to claim  1 , wherein the enforcing on-hook means comprises: 
       a fourth resistor (R 5 ), coupled to a voltage source (Vcc) and a second node (a 2 ) which further connecting to the fourth lead of the photo-coupler (U 1 ) of the overload detecting means;  
       an inverter (U 4 F), having an inverter input terminal coupled to the second node (a 2 ) and an inverter output terminal;  
       an OR gate (U 2 B), having a first OR gate input terminal coupled with the inverter output terminal, an OR gate output terminal to a third node (a 3 ) and a second OR gate input terminal;  
       an AND gate (U 3 A), having a first AND gate input terminal coupled to the third node (a 3 ), a second AND gate input terminal coupled to a fax/modem controller, and an AND gate output terminal coupled to the second OR gate input terminal;  
       a fifth resistor (R 4 ), coupled to the third node (a 3 ) and a fourth node (a 4 );  
       a second capacitor (C 2 ), coupled to the fourth node (a 4 ) and ground;  
       a second transistor (Q 2 ), having a gate coupled to the fourth node (a 4 ), a source coupled to ground, and a drain coupled to both the hook switch and the fax/modem controller.  
     
     
       5. The protection apparatus according to claim  4 , wherein the fifth resistor (R 4 ) and the second capacitor (C 2 ) form an RC charge/discharge circuit to delay a time for outputting the on-hook signal. 
     
     
       6. The protection apparatus according to claim  4 , wherein the second transistor (Q 2 ) forms a switch circuit to switch an off-hook signal output from the fax/modem controller to an on-hook signal. 
     
     
       7. The protection apparatus according to claim  1 , wherein the hook switch comprises a relay. 
     
     
       8. A protection means to prevent a fax/modem machine coupled to a telephone line from being over heated, the protection means comprising: 
       a detecting circuit, for detecting a temperature of a fax/modem circuit and outputting a high temperature signal when the temperature exceeds a pre-determined value;  
       enforcing on-hook means, coupled to the detecting circuit for generating an on-hook signal according to the overload signal and an off-hook signal; and  
       a hook switch, coupled to the enforcing on-hook means and connected to the telephone line in series, for performing an on-hook operation on a telephone according to the on-hook signal  
       wherein the enforcing on-hook means comprises:  
       a resistor (R 6 ), coupled to a node (a 5 ) and ground, wherein the node (a 5 ) further connects to the detecting circuit;  
       a capacitor (C 3 ), coupled to the node (a 5 ) and ground; and  
       a transistor (Q 3 ), having a gate coupled to the node (a 5 ), a source coupled with ground, and a drain coupled with the hook switch and a fax/modem controller.  
     
     
       9. The protection means according to claim  8 , wherein the detecting circuit comprises a thermo-sensitive resistor for outputting the high temperature signal when the temperature exceeds the pre-determined value. 
     
     
       10. The protection means according to claim  8 , wherein the transistor (Q 3 ) forms a switch circuit to convert an off-hook signal output by the fax/modem controller into an on-hook signal. 
     
     
       11. The protection means according to claim  8 , wherein the hook switch comprises a relay.